Greek banks: Why the money’s running out

People wait in line to withdraw 60 euros from an ATM after Greece closed its banks on June 29, 2015 in Athens, Greece.

Pictures of Greeks queuing outside banks on Wednesday have added to the pressure on the country's far-left government to capitulate to its creditors' demands.

After a combination of disastrous borrowing and years of austerity, the country's fiscal situation has become so dire that its banks are shut, citizens can only withdraw 60 euros ($67) a day from ATMs—which are reportedly running out of 20 euro notes—and there are even concerns that pension funds will not have enough euros left to pay pensions.

"The pressure on the banking system is already great and the message to account holders (voters) is already crystal clear. Time has almost run out," strategists at Rabobank warned in a research note on Wednesday.

Capital has hemorrhaged out of Greek banks—but the true effects of this have not yet been felt, because the European Central Bank (ECB) has provided an emergency backstop of funding for financial institutions, known as the Emergency Liquidity Assistance (ELA).

But this is could be under threat, with the ECB's governing council expected to meet in Frankfurt on Wednesday evening to make a call on whether to raise, keep at the same level or cut the ELA.

If Greek banks are seen becoming insolvent, the ELA funding, which has already been capped, could be cut.

Alternatively, the ECB could raise the "haircut" made to Greek government bonds and government-backed assets presented as collateral for funds, as the country is now in arrears over its debt to the International Monetary Fund.

The ECB's action has already led Fitch Ratings to downgrade the issuer default ratings of the four main Greek banks to "RD" (Restricted Default)—which means they have failed to meet financial obligations but are not yet bankrupt.

If the Greek sovereign was officially moved into the territory of a country in default, this could put even more pressure on the banking system and potentially instigate its collapse.